1. Field
The invention is in the field of methods and devices to enable the linking of a computer terminal device to one or more additional terminal devices so that each of the linked devices effectively operate in parallel to receive information from the computer or to input information into the computer.
2. State of the Art
Some computer systems are configured to allow several terminal devices to be connected effectively in parallel so that each of the paralled terminal devices receive identical information from the computer or each can supply information to the computer and to each other. For example if two CRT input/output terminals are connected in parallel in such a system, any information from the computer will be displayed on both paralleled terminals. Also, in most instances either may be used to enter data or instructions into the computer and the entered data or instructions on one terminal will show on the other paralleled terminal.
Most computer systems today are designed to be connected to many terminal devices, such as many CRT displays, with each terminal device operating independently of the other terminal devices. In fact, most systems are designed specifically to prevent terminal divices from being paralleled so that a person on one terminal cannot spy on another terminal and cannot interfere with the operation of such other terminal. With such systems, it is possible to electrically connect two or more terminals together in parallel, but once such electrical connection is made, the terminals are always connected in parallel. Further, unless an elaborate mechanical switching arrangement is used, a particular terminal cannot be easily paralleled to a desired one of a plurality of terminals. Such a switching system is completely impractical where terminals are located at physically separated locations such as in different parts of a city or country.
In many instances it may be desirable to effectively parallel two terminal devices on a selectable basis. For example, if an operator is having a problem with a particular program or particular operations in a program, rather than having a person more knowledgeable in operation of that program or a special program troubleshooter or instructor physically travel to the operator's terminal, or orally describe, such as by telephone, the problem and solution, that person could merely connect his terminal in parallel to the operator's terminal, find the problem, and show the operator the correct procedure. Another example where selectable parallel connection might be desireable is where a supervisor or other official may wish to observe for security reasons what a particular operator is doing. With a parallel connection, the actions of the operator could be monitored unknown to the operator. In such instance, it is not necessary that the effective parallel connection provide for input from the auxiliary terminal, but merely for the providing of the same information flow between the CPU and monitored terminal to the auxiliary terminal. Further, rather than actually observing the operator, it may be desired to actually record and make a record or audit trail of an operator's actions to check at a later time, if necessary.
One computer system in wide use today is the VAX Computer system manufactured by Digital Equipment Corporation (DEC). This system uses what DEC calls the VMS operating system. Such system is different than most systems in use today in that rather than having the drivers for each terminal device a fixed portion of the operating system of the computer so that such operating system must be modified each time a terminal device is added or subtracted from the system, the VMS operating system provides a generalized or terminal independent device driver which is connected through specific or terminal dependent device drivers to specific terminal devices. Thus, it is not necessary to modify the operating system when terminal devices are added or subtracted, but to merely connect the terminal device to an appropriate specific terminal dependent device driver.
There is currently no known way to effectively and easily provide selected parallel operation of two or more terminal devices with such an operating system.